Rotary grinding or drying mill



Jan. 1, 1952 N. HALL ROTARY GRINDING OR DRYING MILL I5 Sheets-Sheet 1 Filed Dec. 29, 1947 S 4 23H 51. m 7 m v n 1 2 W, x y m x x 4 2 Q Q B 5 Ezi 2 a my. 4. my 5:

INVENTOR.

Jan. 1, 1952 N. L. HALL 5 5 ROTARY GRINDING OR DRYING MILL Filed Dec. 29, 194'? 3 Sheets-Sheet 2 VlI/IIIIIIII/IIIII/IIIIIIIIIIIII I 1 1 r I 9 1 INVENTOR.

Jan. 1, 1952 Filed Dec. 29,1947

N. L. HALL ROTARY GRINDING OR DRYING MILL 39 4/ a 40 8 383 A 40a .35 43- a was um /////1/ ://L/L///4///71/ /L/ ////L/////// awaw 3 Sheets-Sheet 3 Fig. 13.

INVEN TOR.

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Fig. 14

ortgmbling mills and in its vg rious, ppli Patented Jan. 1, 1952 This invention relates to cylin clrigal revolving mm se s ahc i s t lr o arryr o s calcining r nqinfira in i ifnavqet s a ba llfor grincligg mill,

Under} h radq amefl i a bal WPs "A l! i s. sed. h rin n r mmi ufi o ks. t essin 1 m qr. ha 19 rmslms w'mat r l o a y powsifi z qr 9 i ei Pulp grinding action l lnni ia l r r lls. a $211!?! crushing elements.

In the following outline the terrr boll mill f is u to. e ot a v lvi li drflq f t qi. receptacle in whicl alfreelyjtugilplipg 'c t q loagl is under redl otio n from tl e gfringin qr rvu h r of h mblia mill' a drsf h a term t'pplying to alm illusir g balls or pepb a ndi e m hq tqmal 1. 2m in, the millfbeing fundamentally; r ri' la r 7 Ball mills have been developedonqer a var i et;

of cro ss sectional sl apes sugl irassinglelq ders of-cylindr-ical or coniyal; b ar r ape of multiple l nd w rev n 'arpnndv. a 9 in axis, or of a i le ylinder with. inglqien tudinal division wall plaeed digrr etrplly u the mill to divide its: interior irltor tyv, cylindrical compartments, as outlined irii Letters Patent 0f-the United States #1 ,315, 770, refer ence being particularly maqe to tl 1e la tter type of ball mill, hereinafter referreg to as a "c0fn pzg-rtment mill." Other applications of" the corn partrge t mill can be made for service sujehe s 9, h qrigor tal rotary drier, wherein a developegi 'l ested gas is ass hr h. ar l hs ylim im neous ly with a transientlgad whioh ispgsslr g, either parallel ofcguriterclirrerit tolthe fiqfi of' gas so that in passing the load't l ro ugh 'tfieoyl inder it isacted upon by the heted gl2ses to develop a dewatering or drying, a qalcir1'atiom' 2 Claims; (01. 241 1 37 or, an incineration of the load. Thevarioiis ap plications, are treated in their" order iii the-folowi ldes rint o r i is teiiqe-i lmade jtheawompamz-in r w 25%: 911 form; a art oi these. specifi atio 2. th m numera s m le i o im lar Pan s: n,

ws end wherein;

, presents a long ituding l vertical seqmb m entba im it- 11? 99 3 i w in 2' erti al. fnq' li isiia" K swxdss s ti fisk mu qf. Figure 1, n2 a frggmentgry portion of the; ni f ii viii's my il l l nt Figure 3 shows g side edge view oi a se etior e l Figure lii is across secuqgia; t l e rotary drier taken on line- |5l5' of-Fiuie 12. H

Referring to the drawings: A cylindrical shell I is provided with heads 3 attached thereto by bolts 2, the heads being provided with hollow trunnions 4 which revolve in the bearings 5, the cylinder being driven by the attached gear 6, operated by the gear pinion l which in turn is driven by the drive shaft 8 and which can be operated by any suitable motive power.

Supported on the feed trunnion 4 at the feed end of the mill is the scoop 9 which in its revolution picks up and then delivers the feed to the mill through the hollow feed trunnion 4, the feed being advanced along the trunnion by the internal thread screw H) which revolves as a part of the feed trunnion 4. After passing along the mill the load is freely discharged through the discharge trunnion 4a.

To withstand the abrading action received from the falling load within the mill, the heads 3 are provided with liners H and the mill shell is likewise protected from abrasion and load wear by the circular lining rings I2 which are placed within the cylinder by virtue of removing one head of the mill and collectively several rings line the entire inner circumference of the mill shell.

Diametrically across the liner [2 is placed the compartment wall l3 as illustrated in Figures 3 and 4 and as assembled in Figures 1 and 2. As shown in Figure 5, the compartment wall is left open on one side edge at M to allow for a free fall of the feed on entering the mill as it is being discharged from the feed trunnion 4. At the discharge end of the mill the compartment wall is discontinued before reaching the mill head at the space I5 and which allows the mill loads on each side of the compartment wall to join in common before being discharged from the mill through the hollow discharge trunnion 4a. Also, the com,- partment wall is interrupted in continuity along its length by providing'space I6 between two sections of the wall l3, this space providing for a free fall through the wall of a portionvof each compartment load as it advances along the-mill and serves to develop a balancing and intermixing of the compartment loads in addition to the provision provided at spaces l4 and i5.

' In Figures 6 and 7 the mill sections are shown with the compartment wall being in a horizontal position to illustrate an outline of the mill load when it has taken its repose in slope when either out of action, or, when starting to slowly revolve as the mill is being placed into operation. The mill load H, which is shown above the compartment wall [3, falls over the end edge of thewall and joins the load l8 which is below the wall, thus placing the mill load in a larger proportion below the wall. It can also be noted in Figure 6 that the screw thread H) on the interior of the feed trunnion 4 has a single point of delivery for the advancing feed and which would deliver the feed on one side of the wall l3 more than the other. As hereinafter further explained, unequal mill loads under momentum can not easily be corrected to a balanced position, and as shown in Figure 10, with the compartment wall in a vertical position, the mill half loads may reach the same hydrostatic level within the mill but one half load may have a greater ball load or a V greater proportion of grinding media as shown at I8, and the other half load a lesser proportion as shown at ll. It is apparent that an easily flowing feed, such as a liquid pulp, would have a tendency to pass through the mill interior in the space of least resistance to its flow or through the compartment which had, the small complex load as at I'Id rather than through I811.

In all cross sectional figures the mill rotation is considered as turning clockwise.

Referring to Figure 8 showing an outline of the mill load while operating within the space l5; the speed of the mill is advanced to bring the load speed just under the centrifugal effect necessary to carry the load over the zenith of the mill interior, thus allowing the load to descend in-a cascade until it again reaches the toe of the load'against the opposite side of the mill shell where it joins the mill load and ascends as before.

The movement of the load in the space I5 is similar to the action which is developed in a plain mill, that is, one without a compartment wall. As noted by the broken arrow outlines of the load in Figure 8, the load is lifted with the revolving mill shell and in its momentum ad vances to a position which is almost the zenith of the mill interior whereupon it opens as a crest and descends as a cascade where it again meets the mill shell at the toe of the load and then reenters the load and continues as before. That portion of the load which is away from the mill center and near the shell is ascending, 15a to I51), whereas the cascading portion of the load above it, I5b to [5a, is' descending and develops what could be termed a shear zone, [50 to 15d,

. ment of time is involved for the development of that change. The advancing movement of the mill precludes such an element of time. V

The practical perimetrical speed of a mill load in a large ball mill is about 384 feet per minute. Such a speed will allow the centrifugal effect of the load to break at the crest, after which the effect of gravity will develop and the load will descend in the desired cascade. A speed of 410 feet per minute will developa centrifugal effect which will carry the load over the zenith of the mill interior, cause the load to open without the desired cascade and scatter as a rain in falling. The desired operation is, to keep the mill load with a definite cascade of the falling portion resting upon the ascending portion of the load, thus developing a definite shear zone within the load.

By the use of a compartment wall placed diametrically through the mill there is a decided change of conditions governing thetumbling mill load.

When the mill revolves and the wall meets the load, that is to say, one half of the total load of the mill, it starts to lift the load towards the zenith of the mill interior and when the ze' nith is approached it drops the half load in a substantial body and through practically the maximum cross sectional space within the mill. As this load falls it drops in its entirety, substantially as one mass, the mixture of the mill load being uniformly distributed. The half load falls with a general impact, of a general mixture, and through substantially the maximum space within the mill, and as this load falls, the air within the space below the load passes through the load in displaced position. The fallen half load is then at'the nadir of the mill interior and in 5 its continued revolution within the" mill, it follows the advancing side of the compartment wall and rises but just before again reaching the zenith of themill interior it again falls behind the wall-for it has no supporting wallas in the previous fall-to a position which is principal- 1y against the rising side and opposite "end of the-wall, accordingly, each half load acquires two falls for each revolution of the mill, the main fall being of the load in its position above or before the wall, and the secondary fall being in a position below or following the wall. Referring to Figure 9, the dash line approximates the travel or orbit of each half load in one revolution of the mill, the primary fall being of the load when it is above thecompartment wall, as noted by the arrow points I9 to I9a, and the secondary fall in its position below the Wall, as noted by the arrow points to 20a.

In itsre'volution'with the mill the momentum of the mill load and the time required for overcom ingthe inertia of that load when acquiring a gravity fall determines the position ofkthe mill and compartment wall when the load falls will take place. Under the required speed, the time of maximum fall of the loadwhich is above the wall, will take place during the passing of the compartment wall within 20 either way of the vertical mill center line, and in ascending, the load which is below the compartment wall will descend and fall as at 20 and 20a, principally against the ascending side of the wall as at 2!. When the load is circumferentially advancing under a momentum any change in its direction of movement involves an element of time for It the acceleration of such change. The advancing movement of the mill load overcomes a time required for a change of directional movement of the load parts. The load does not slide over the wall in reaching its lower positions and the s points of wear of the mill interior are principally on the mill lining at'a position about from the advancing end of the wall, as at -22 and, secondarily, on the side of the walln ar to the shell "as it rises as at'2 I, a similar action taking place'on the opposite side of the shell and wall "d'uringthe next half revolution of the mill.

The mill half loads do not fall simultaneously -but the load opens and closesin falling and as each half 'load falls itintermixes and changes position "with the air of the mill interior. The llbhd'sfalLWith a squash rather than a definite iimpactanduhave "a general change of position of i'ts components with each fall. V The forces involved in a mill load under action are, centrifugal, centripetal, and gravitational. The revolving movement of the mill receptaele develops a centrifugal force within the l load 'which is reacted upon by its centripetal forcegoverned through the receptacle structure andwhichopposes the'centrifugal action. Ball 'm'ill sspeeds are maintained to develop a centrii ug'al action which is below that required to carry-the mill load to'the full zenith of the mill interior and in a mill of plain receptacle without a 'eompartment walha wave crest is formed and beiore=reaching the zenith of the mill interior the-loarf'topsand then cascades over the surface -01 th'e loadto its'lower position where it reaches the toe of the load, combines, and ascends as be Lfore and as illustrated in Figure 8. In a com- ,zp'a'rtment mill the load is under a similar centrifngaL-action but due to its supportzfromthe compartment wall it is carried past'thezenith wi the ,lmillwiinterior, likewiseguanr element of time centrifugal action and this element of time mitigates against any extraneous longitudinal movement of the load parts.

Centrifugal action on the load parts is at a maximum towards the mill load perimeter and at a minimum at the mill center, and due to the fact that the centrifugal force near the mill center isnegligible, no time is required for over coming it and the load parts start a gravity movement downward without a loss of time and under a full freedom of acceleration in falling, accordingly, that part of the load which is towards the mill center starts its unrestricted gravitational downward movement firstand develops an opening movement through the load successively towards its perimeter near the zenithof the mill interior. The load does not fall as a solid mass but opens and closes in its falling actions, intermixing with the air-of the half mill chamber.

Mill loads within the mill are masses of considerable weight and its parts are not easily displaced, and when under momentum, the resist ance to displacements of the load parts becomes more stubborn, each part being held in its circumferential and gravitational path by a similarly acting body closely adjoining, and when or any reason the loads on either side of the compartment wall become unbalanced and of different size, the longitudinal mobility of the-mill load parts is not always sufiicient to pass the unequal parts of the mill load around the ends of the compartment wall to efiect an equalization of the half loads, and the heavier parts of the mill load, such as the ball load, will remain in unbalanced proportion on either side of the compartment wall, and when this condition exists, particularly with a load undergoing wet grinding, the liquid portions having a less resistance in their flow through the mill will pass through on the side of the mill where there is a smaller ball load and a greater proportion of liquid pulp, accordingly, the mill pulp will pass through the mill without securing as full a crushing action as if both compartments were filled with similar ball loads. A provision ior the constant balancing of the mill half loads is required. Such a provision is provided'by placing openings or space I6 in the compartment wall so that as the half loads are acting {with the mill revolution, aportlon of the load on each side of the compartment wall can pass through to the other side and enter the adjoining half load, thereby maintaining a circulation. between the mill half loadsin addition to the end wall provisions, at I 4 and I5.

The cross section of the load body been [revolved ina plain mill action, as shownin Figure 8v well blankets thehalf load adjoining which is behind thecompartment wall and obviates a free passing of half load parts aroundthe wall for a balancing effect. As shown in Figure 6, the part of the load I! which passed through the slot I5 to form theload part below, [8a, was revolved as a plain 'millaction due to the frictional infiuence of the adjoining dischar ehead of the mill, whereas, that part of the load I! which passed through the space I6 had a free and unobstructed fall through the wall I3 to join the part of the half load at I8b, for the conditions influencing the load adjoining the slot I8 were uniform both radially and longitudinally on each side of the opening.

When a-plain mill is placed in operation there sis a constant and steady peak load'placed upon the operating motor due to the fact that the center of gravity of the mill load is under a constant leverage and there is a load lift on the motor almostwithout variation.

When a compartment mill is placed in operation there is a high peak load during the first revolution of the mill and until the time when the load slides to its lower position whereupon the loading on the motor is relieved and the motor picks up a speed which is transmitted into the mill loads so as to give them a momentum which carries them to the zenith of their actions, whereupon the loads again fall to their lower position, relieving the motor again and during the second revolution of the mill it practically reaches the full speed required for continued operation. The loading placed upon the motor by the falling half loads is intermittent and the inequalities 1 developed by the varying load lifts is compensated and balanced by the mill weight and mass 7 so that the operation of a compartment mill is easier on the motor than is the operation of a plain mill with its constant leverage of load lift.

The conditions governing the passing of the load parts through the space If: at the end of the wall-and the intermediate space l6 are decidedly different. The moving load within the space l5 virtually blankets the adjoining load which is in the compartment sections so that a larger half load on one side of the wall can not pass around the end of the wall to equalize and balance a smaller half load on the other side. At the in termediate space IS the compartment wall lifts a half load a portion of which can pass through the space or slot to the section or compartment below, and do so in a free and unrestricted fall, for the space below the wall is temporarily vacant. There is thus provided a constant intermixing means for adjusting and balancing the -,i:wo half loads both as to size and composition.

Small tramp balls discharged from a plain mill ;show a well rounded and worn shape but similar ballsdischarged from a compartment mill are broken sharp and are cracked in a wedge, pie-cut Ballmills carry a heavy load and have lengths which are seldom more than twice their diameters. Tube mills have similar loads and are of longer length up to four and five times the diamleter, whereas, rotary driers carry light weight loads and have lengths which are generally ten times their diameters. The proportions of the two are extreme to each other but their internal action is fundamentally similar although the mills are used for different purposes. r I

In adapting the compartment mill for use as. a rotary drier the first consideration to be made is with regard to the mill speed of revolution. A ball mill of six feet diameter would have a speedof about 24 revolutions per minute, whereasj a plain rotary drier of the same diameter would have a speed of from 6 to 8 revolutions per minute. The ball mill speed is maintained to develop proper cascading of the load but the drier speed is regulated so that the internal lifters of the drier will carry over and spill the load through the heated gases passing through the' chamber.

Modifying the drier to the compartment feature places a different construction upon the mill action.

Referring to Figure 12 wherein is illustrated a longitudinal section through a rotary drier combination of equipments: A fuel supply pipe Ma, delivers fuel such as oil or gas to the burner 4|,

fire brick lining 40a, resting on a base 40b, set

on rollers 400, which travel on the track-40d, so that the firing hood can bemoved away from the furnace for entrance to the interiors for repairs or other'purposes, or, for regulating during operation the amount of air passing into the stationary furnace 38 with its fire brick lining 38a, setting on fixed foundations 38b. The ignited flame developed at the burner M is designed to develop a complete combustion within the furnacebefore the heated gases enter the rotary drier, otherwise the-gases of the fuel would improperly mix with the fumes developed in the drying operation, and the length of the furnace is designed to meet such conditions of combustion. A feed chute 39 penetrates the furnace 38 so that a delivery of feed can be made to the revolving rotary drier la, such a drier being composed of an elongated hollow cylinder, with or without heat insulation lining, open at'both ends and riding on riding rings 30 attached to the shell by spreaders 3|, all revolving on movable rollers 32 supported at stationary bearings 33. A driving gear 6a, is attached to the mill shell and is operated'by the pinion Ia, which is directly driven by the motor 34. The first section of the drier is supplied with load lifters '35 to receive feed from the feed chute 39 and operate to break up the feed and carry it over in its approach to the compartment wall l3a, which is developed in sections being attached to lugs 36 arranged as a part of and opposite sides of the mill cylinder, the compartment wall or plate being attachedthereto by the bolts 31. The discharge end of the drier delivers the feed to a stationary discharge hood 42, the feed product dropping to the screw conveyor 42a, for suitable delivery. The discharge hood is further supplied with a suction fan 43 operated by the motor 44, the draft from which draws the heated gases through the drier; carries the light weight feed forward and delivers the dusting particles in the gases through the discharge conduit 45 and delivers them to the cyclone dust collector 46 where the exhaust from the system reaches the atmosphere at the outlet 46a, the finer dust settlin r collection at the cyclone gate 461)..

The suction fan 43 affords the chief motive for the migration of the load through the revolving mill and for the removal of the vaporsbeing passed off by the drying load. The revolving cylinder can also be given a slope approximating one half inch per foot of length of the mill to assist the fan in the migration of the load through the mill, also for clearing the cylinder of its load when the fan is out of service.

The rotary drier ordinarily does not have an insulating lining for the feed load is non-abrasive, is light in weight, and the heat developed by the furnace is designed to be closely compensated by the vaporization of the moisture so that its heat value is perfectly absorbed in the drying operation. A furnace gas with an entering temperature close to cherry heat would be reduced or absorbed so that the discharging feed would have a temperature well under the boiling point. Similar to ball mill operation and design, the compartment wall in a drier requires a compensation and balancing feature for the mill loads and for this effect the wall space l6a, is provided and in addition half length spaces [61), and 1.60, the wall being shown in section 1311 in Figure 14, and i317, in Figure 15.

The compartment wallfeature'eliminates the need for lifters, such as 35, and under the same principles as outlined for the ball mill, the compartment drier utilizes the falling half loads to pass through the gases of the mill interior so as to develope an intimate contact between the feed and the transient gases. The compartment drier places a greater load upon the suction fan for the additional draft required and for the fact that the contained vaporized moisture within the cylinder is under a greater density and compression and its more rugged control is required to pass its expansion to the atmosphere at the cyclone discharge.

The agitated contact caused between the feed passing through the drier gases develops a more rapid drying and results in a rotary drier of increased capacity.

In a plain mill drier, the load occupies one portion of the cross sectional area of the cylinder and the gases another, the upper portion. An increase of mill diameter to secure a greater capacity of product is limited by the gravity effect of the spilling load and there is a definite relation and limit between the diameter of the mill and efllcient drying reactions. The compartment drier is not limited to such conditions, for the actions of the falling half loads as they are being passed through the gases at each fall makes the drying contact between the load and gases intimate and positive, for the load constantly contacts the gases at each fall regardless of the diameter of the drier cylinder. Also, the falling load receives an impact which develops a uniform drying effect upon the small particles of the mill load, such an impact being violent in comparison to the limpid spill of the load of a p ain mill as it passes over and falls from the lifters.

An opening in the compartment wall for purposes of equalization of loads should preferably extend from one perimeter directly across the mill to the opposite side, or, from the mill center to either perimeter. An opening in the wall such as an aperture has a variable effect in passing feed through the wall from one side to the other according to the amount of load in the mill, whereas, a slot opening extending from the mill center towards the perimeter is effective under all proportionate loadings.

The compartment mill feature can be applied to several operations, such as for ball, pebble, or tube mills used for the fine grinding of ores or cements; for rotary kiln used for the calcination of ores; for rotary driers used for the dehydration or drying of pulps or meals to develop stock foods; and, for the rotary waste incinerator wherein the mill actions develop opening contacts to assist in the combustion of material with a minimum of smoke and smog. The compartment mill actions in all of these operations are fundamentally similar.

I claim:

1. A horizontal rotary mill comprising: a cylindrical casing having openings at both ends for receiving and discharging material; and a wall 10 within the casing lying substantially in a diametral plane and extending across the full diametral width of the casing and longitudinally for the major portion of the length of the casing to divide the interior thereof into two compartments; said wall being provided with an opening intermediate its ends extending across the full diametral width of the casing to provide for free passage of material by gravity through said opening from each compartment to the other during rotation of the mill.

2. A horizontal rotary mill comprising: a cylinorical casing having openings at both ends for receiving and discharging material; and a plurarity of longitudinally alined wall sections within the casing lying substantially in a common diametral plane and extending across the full diametral width or the casing and longitudinally for the major portion of the length of the casing to divide the interior thereof into two compartments; said wa.l sections being spaced apart longitudinally to define an opening between each pair of adjacent sections extending across the full diametral width of the casing for free passage of material by gravity through said opening from each compartment to the other during rotation of the mill.

3. A horizontal rotary mill comprising: a cylindrical casing having openings at both ends for receiving and discharging material; and a wall within the casing lying substantially in a dametral plane and extending across the full diametral width of the casing and longitudinally for the major portion of the length of the casing to divide the interior thereof into two compartments; said wall being provided with an opening intermediate its ends extending radially the full distance from the axis of the casing to the perimeter thereof to provide for free passage of material by gravity through said opening from one compartment to the other during rotation Of the mill.

NEWTON L. HALL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 420,934 Graepel Feb. 11, 1890 1,062,946 Bahler May 27, 1913 1,217,351 Schwarz Feb. 27, 1917 1,290,178 Hachtmann Jan. 7, 1919 1,315,770 Hall Sept. 9, 1919 1,557,475 Vogel-Jorgensen Oct. 13, 1925 1,650,508 Goebels Nov. 22, 1927 FOREIGN PATENTS Number Country Date 85,054 Austria Aug. 10, 1921 469,142 Great Britain July 20, 1937 371,883 Italy July 7, 1939 666,019 Germany Oct. 8, 1938 524,029 Great Britain July 29, 1940 

